As a child, you might remember hearing “lights out” as a way to tell you it was time to go to bed. Having the lights off at bedtime is much more than a common bedtime phrase, though. In fact, the decision to turn out the lights — or leave them on — could affect your health.

Yet the problem lies beyond ceiling lights and lamps. Light surrounds us from multiple sources, including streetlamps, televisions, and the blue light emitted from our electronic devices, like cellphones, computers, and tablets.

Sleeping with any lights on is considered detrimental to getting a good night’s rest. Subsequently, not getting enough quality of sleep can lead to numerous health consequences. If you’re considering leaving a light on at bedtime, consider the following repercussions.

Exposure to light during sleep makes it difficult for your brain to achieve deeper sleep. The more shallow or light sleep you get at night, the more your brain oscillations (activity) that allow you to get to deeper stages of sleep are negatively affected.

Aside from conditions that directly affect your brain, a lack of deep sleep from light exposure has also been linked to the following side effects.

Depression

Sleeping with the lights on has been linked to depression. Blue light from electronic devices may have the worst effects on your mood.

A lack of sleep can also cause moodiness and irritability. Children who don’t get enough sleep may be more hyperactive.

Obesity

One study on women found that obesity was more prevalent in those who slept with a television or light on.

Study participants were also 17 percent more likely to gain around 11 pounds in 1 year. Lights on outside of the room were found not to be as large of factor compared to light sources inside the bedroom.

One factor in lack of sleep-induced obesity could be food intake. Studies have shown that the less sleep you get, the more food you’ll likely eat the next day. This can affect the timing of your meals, too — eating late at night may lead to weight gain.

Accidents

Not getting enough quality sleep makes you less alert the next day. This can be especially dangerous if you drive a car or other type of machinery. Older adults may also be more prone to falls.

Increased risk of chronic illnesses

If light continues to interfere with your sleep in the long term, you could be at an increased risk of certain chronic illnesses, whether you have obesity or not. These include high blood pressure (hypertension), heart disease, and type 2 diabetes.

Sleeping with the lights on may be beneficial if you’re trying to take a quick nap during the day and don’t want to fall into a deep sleep. However, this technique still doesn’t lend itself to quality of sleep.

Nightlights and other light sources may be helpful for young children who might be afraid of the dark. As children get older, it’s important to start weaning them off of light sources at night so they can achieve better sleep.

Overall, the risks of sleeping with the lights on outweigh any possible benefits.

While it may seem like you don’t have time for a lot of sleep, getting the right amount — and the right quality — of nightly shut-eye will dictate your health, both in the short term and in the future.

Sleep helps to:

  • repair your brain and body
  • allow muscle recovery
  • fight illnesses and chronic conditions
  • put you in a better mood
  • help children grow

When you’re exposed to light at night, your body’s circadian rhythm is thrown off. As a result, your brain produces less melatonin hormones that otherwise allow you to get sleepy.

Light exposure before or during bedtime can make it difficult to fall and stay asleep because your brain won’t make enough sleep-inducing melatonin.

Even if you do manage to fall asleep with lights on in your bedroom, you may not get enough rapid eye movement (REM) sleep. The other stage of sleep is non-REM, which includes light sleep and deep sleep.

While light sleep is important too, not spending enough time in the other two sleep cycles won’t allow you to get the full benefits of a good night’s sleep.

Your brain needs to spend about 90 minutes at a time in each cycle.

While some children prefer to have a light on for comfort, many adults are guilty of keeping lights on, too. Perhaps you’re used to keeping a bedside lamp or television on at night. Or maybe you look at your phone or tablet.

It’s difficult to go without lights off in your bedroom when you’re used to having them on. You can start by using a small red-emitting nightlight, and then get rid of that once you’re used to the darkness.

It’s been found that red nightlight bulbs don’t have the same detrimental effect on melatonin production as other colored bulbs.

It’s also important to incorporate other healthy sleep habits into your routine so you won’t notice the lack of lights:

  • Use room-darkening blinds.
  • Start lowering the lights in your home before bedtime.
  • Go to bed at the same time every night, waking up at the same time every morning.
  • Keep electronics out of your bedroom.
  • If you must check on an electronic device, wear blue light-blocking glasses to retain melatonin.
  • Avoid daytime naps, if you can help it.
  • Exercise earlier in the day, such as in the morning or afternoon.
  • Avoid alcohol, caffeine, and large meals at night.
  • Commit to a relaxing bedtime routine, such as reading, bathing, or meditating.
  • Set your thermostat to a cool temperature.

Once you wake up in the morning, make sure you seek light — either artificial or natural — as soon as you can. This will eventually set the tone for your body that light equates to wakefulness, while darkness means it’s time to sleep.

Sleep quality is dependent on a dark, quiet space. Sleep deprivation can quickly become a dangerous slope to bad health that goes beyond simply being cranky the next morning.

Therefore, it’s time to start sleeping with the lights off. If you or your partner have difficulty with sleeping in the dark, gradually work your way into it with the steps above.

If you still don’t feel like you’re getting enough sleep, see a doctor to rule out other issues, such as sleep apnea or insomnia.